Food emulsions have been widely used as delivery systems for nutrients. In elderly and dysphagia diets, thickened foods containing hydrocolloids such as xanthan gum (XG) are widely used to prevent miss swallowing. These thickeners not only modify the rheological properties of liquid foods but may also influence their digestive characteristics. It is therefore important to clarify how the addition of the XG sol affects lipid digestion in emulsions. Conventional studies have mainly used monomodal emulsions, which makes precise control of lipid digestibility difficult. Recently, we proposed a food emulsion blend (FEB) prepared using two monodisperse emulsions with different droplet sizes. In this study, we investigated the in vitro gastrointestinal digestibility of FEBs mixed with XG sols.

Oil-in-water emulsions were prepared using 1.0% (w/w) Tween 20 aqueous solution as the continuous phase and refined soybean oil as the dispersed phase. Monodisperse emulsions were produced via premix membrane emulsification equipped with tubular Shirasu porous glass (SPG) membranes (mean pore sizes (d_p): 1.1, 10.0, and 50.4 µm). Two emulsions with different droplet sizes were mixed in equal volume to prepare FEBs. Thickened aqueous solutions were prepared by dissolving 1% or 5% (w/w) XG in Milli-Q water containing 0.05% (w/w) blue dextran and stirring for 30 min using a homomixer For in vitro gastric digestion, FEB (7.5 mL), thickened solution (7.5 mL), and simulated gastric fluid (15 mL) were incubated at 37 °C under shaking (115 strokes/min) for 2 h, followed by intestinal digestion with an equal volume of simulated intestinal fluid at 37 °C for 2 h. Particle size distribution and free fatty acid (FFA) release rate were measured, and droplets during digestion were observed using a fluorescence microscope.

FEBs mixed with 1% XG sol (1%XG-FEB) were macroscopically homogeneously dispersed in the simulated gastric fluid and remained as a liquid phase after gastric digestion. In contrast, the samples mixed with 5% XG sol (5%XG-FEB) did not disperse macroscopically homogeneously, and fine lumps were observed during gastric digestion. The 1%XG-FEB maintained its bimodal particle size distribution during gastric digestion. This stability was likely because of interfacial coverage by Tween 20 and XG. For the 5%XG-FEB, a new peak appeared in the 100–2000 µm range after gastric digestion, suggesting the formation of XG-derived aggregates. The distinct bimodal droplet distribution of the FEBs disappeared during intestinal digestion. FFA release profiles varied depending on the droplet size combination. In the 1%XG-FEB, the maximum FFA release after 120 min (φ_max) ranged from 28.6% to 39.6%, showing a positive correlation with the total droplet surface area. In contrast, in the 5%XG-FEB, φ _max ranged from 34.2% to 40.9%, but no correlation with surface area.

These results suggest that FEBs stabilized with a low concentration of XG have the potential to control lipid digestibility through the combined effects of droplet structure and system viscosity.

This work was partially supported by the Japan Society Grants-in-Aid for the Promotion of Science (JSPS) KAKENHI Grant Number 25K00192, Japan.